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Carving Brainteaser

post #1 of 63
Thread Starter 
For some of you Bob B and others this won't be a challenge at all so shhhhh!

Ok, some teaching systems are now apparently trying to eliminate rotary.

On a set of skis, I (and any other long-time skier) can lay down several different radius arcs . . . purely carved. Now if when you put a ski on its edge, the sidecut then is the only thing dictating a *purely carved* turn - then how is is possible for us to make a variety of sizes of razor sharp arcs on the same pair of skis?
post #2 of 63
Tip the ski, Turn the ski (rotary) and monitor pressure. These have been the three tenets of skiing since the Nords invented the thing! How do you eliminate rotary?

I'll keep quiet on the pop quiz for now.

Spag's quote of the day:
"Y'know what? I'm sick and ****ing tired of you calling me 'Meat'."
- Eppie Calvin "Nuke" LaLouche (Tim Robbins) in "Bull Durham" -<FONT size="1">

[This message has been edited by Notorious Spag (edited July 27, 2001).]</FONT>
post #3 of 63
I guess it's not fair for me to answer this one either. Good one though Todd... (biting my tongue)
post #4 of 63
Hmm. Perhaps, after you start the kinetic chain process in the feet or ankles by putting your skis on edge, varying degrees of rotational angles of the hip joints would determine the different shapes/arcs of the turn.

I think. but what do I know?

------------------
Be Braver in your body, or your luck will leave you. DH Lawrence
post #5 of 63
The greater the edge angle, the greater the distance the center of the ski must flex to contact the snow. This makes the contact line between the ski and the snow have a shorter radius, so the turn has a shorter radius. So varying the edge angle will vary the turn radius. As someone once said: "I think this involves a cosine somewhere."
post #6 of 63
To illustrate more, I'm thinking of the image Bob B. once gave of the bar stools. I believe he calls it the fulcrum mechanism? So the degree of rotation combined with torque or twisting force of that rotation would effect turn shape?
post #7 of 63
Crudmeister, Lisamarie, Gonzostrike...Pressure CAN affect the radius of a turn... all things being equal. Try not to think of pressure as something that you DO, however. Think of it more as something that you distribute, re-direct, and control/monitor. Sometimes people get carried away with PRESSURING a ski and instead end up driving too far forward and LEVERING instead. Important difference. Also, without tipping or turning to get this pressure thing going, all you've got is a straight run while lengthening and shortening the body.

Edging or tipping the ski (and the degree to which you do it) will also affect radius. Edging without pressure control and rotary, on the other hand... you'll just flop over on your side. (How many of you have spent the morning on snowblades and switched to skis? Try it sometime!)

Finally, the amount of rotation applied to the column of the leg will have an influence on the radius of a turn. Without tipping and pressure control, we skid uncontrollably. Or maybe not... you'd just look like a mannequin (sp?) spinning around in circles as you slid down the hill.

The blending of the tip/turn/pressure control skills in diffent "ratios" (for lack of a better word) can have a dramatic effect on radius. These are just some of my own personal guidelines and even I don't consider them law. They tend to evolve season to season... some seasons I move backwards!!! My question still stands... How do these "teaching systems" hope to remove Rotary from the equation and still develop a well rounded skier? I'm not pointing fingers here. I'm, curious to know.

Spag's quote of the day #2:
"What's wrong with lumber yards? I own two lumber yards."
"I notice you don't spend too much time there."
"I'm not exactly sure where they are."
- Ty and Danny in "Caddyshack" -

ps. I'm watching Caddyshack right now. Gotta go. Carl's about to blow up the golf course!<FONT size="1">

pps. BB must've been about 30 seconds ahead of me. I didn't realize that rotary wasn't part of this exercise. Sorry All! Must've got all excited.

[This message has been edited by Notorious Spag (edited July 27, 2001).]</FONT><FONT size="1">

[This message has been edited by Notorious Spag (edited July 27, 2001).]</FONT><FONT size="1">

[This message has been edited by Notorious Spag (edited July 27, 2001).]</FONT>
post #8 of 63
crudmeister yes.
in "the art of carving" there is a little template model you can copy and make a "shaped ski" and see for yourself.. <FONT size="1">

[This message has been edited by dchan (edited July 27, 2001).]</FONT>
post #9 of 63
This was a question I took to the Acadamy. No one there could give a satisfactory answer. I found the answer in Ron LeMaster's book The Skiers Edge. Gonzostrike is on track. It has to do with the "steering angle" at the tip of the ski and how you pressure it. In fairness, Ron didn't have time to discuss this with me.
post #10 of 63
Today I thought up this question that I think might fit here. I was going to start a new thread but this seems the place for it.
When you carve a 360 with railroad tracks, does rotary occur?
My opinion: In the words of a past President:"It depends on how you define...." rotary. If it's "steering" I'd say no. But if there's turning then some kind of rotary has to be involved.
post #11 of 63
Thread Starter 
Good additions BobB! Actually I didn't intent to eliminate rotary from the equation - I phrased it poorly. I was mentioning that some systems believe there is no rotary is a purely carved turn - but didn't say whether or not I believe this is the case. No I just was interested in open discussion on since some people think that a certain sidecut will only carve its "built in" radius, why then we can actually pure carve a wide variety of turn sizes with the same skis. Which is why I'm always saying "more sidecut = more choices" because a deeper sidecut does allow even tighter carves - but does not eliminate also making carves of the exact same radius as skis with less sidecut.

Anyways - this is turning into a good thread!
post #12 of 63
Todd, thank God you clarified the rotary bit! I didn't quite feel you were posing the question wtih the absence of rotary.
By definition of course, there are no "pure carved turns" as that would imply the complete absence of skidding, a turn devoid of any lateral displacement.
Whether a conscious or intuitive (see the Mahres)activity, active guidance through the arc is there. Long live rotary in its correct proportion and relationship to the blend!!
post #13 of 63
Robin,

Does lateral displacement require skidding? Or did I misunderstand...

I used to believe no true carved turns existed, until the last few years after following distictly ice-skate like ski tracks on hard snow, and watched people actually vary turn size while leaving the same type of tracks(Not park'n'arc either).

Rotary input does not necessarily cause skidding(IMEO). <FONT size="1">

[This message has been edited by Roto (edited July 28, 2001).]</FONT>
post #14 of 63
Thank you for the clarification. I didn't think you were eliminating rotary from the equation. This IS turning very interesting. Gives us ideas about different possibilities.

------------------
Be Braver in your body, or your luck will leave you. DH Lawrence
post #15 of 63
Is it just me or does anyone else have a problem with the term 'radius' applied to turns? Some people seem to think the term radius is directly interchangable with the term arc. Is that a separate thread?

Sometimes I wonder if the numbers relating to radius-of-sidecut are really the length of the arc or vice-versa.
post #16 of 63
Roto, I guess this is why I tend to "steer" my way away from getting trapped in the technical aspects of the forum. The language is confusing at best. What I mean by lateral displacement is the ski breaking away from it's intended arc.
Of course, most of the tracks we see in snow is where consistent feedback is available for effective, accurate, positive movements. Bulletproof or freshly tilled corduroy allows that, but under normal varied conditions, skis chatter, bounce etc. We are caught in balance challenges, leveraging or inadequately monitoring pressure or edge, fall victim to imprecise steering, blah, blah.
Like a learned colleague stated, "carving is more an intent than event". Rotary does not cause skidding, negative movements do, if the intent was to carve.
See I told you these discussions were convoluted! In the skid/carve continuum, the distictions get blurred at the extremes. But reality conspires against pure carving. Inconsistent deflection of the skis and pilot error do not allow for perfection or purity. Reality sucks. Great concept and discussion though!!<FONT size="1">

[This message has been edited by Robin (edited July 28, 2001).]</FONT>
post #17 of 63
Gonzostrike, Yes I agree. I was just including you three in the post because you were the first 3 to go to each different movement pattern in search of the answer. I've been in Denver for two days so now I've got some catching up to do. Toodles!

Spag's quote of the day:
"If the VP is such a VIP, Shouldn't we keep his visit on the QT? Because of word leaked from the PA and got to the VC, the VP could turn up MIA and we'd all end up on KP."
- Robin Williams in "Good Morning Vietnam" -
post #18 of 63
I hate to keep obsessing on all this kinetic chain stuff, but one of the "catch phrases" for fitness trainers who are interested in developing sport specific programs is "Train the Chain". So when you say:

"Nonetheless, for the sake of this discussion, I maintain that it is possible (if not usually advisable) to vary the radius of a carved turn without any active, muscular rotary input to the skis. This is a theoretical discussion only, because I also maintain that good skiers invariably blend in appropriate rotary skills to each and every turn. But it is possible...."

The first word that comes to my mind is the word "TORQUE". Because if the movements of the chain do not follow through to a minimal degree of rotation, the knee is a vulnerable point.
A ballet dancer can "fake" a turnout by simply moving her feet into position without any rotation at the hip. This is great business for physical therapists.




------------------
Be Braver in your body, or your luck will leave you. DH Lawrence
post #19 of 63
Bob B

>>I think that that is the heart of this whole discussion: does the radius of the circle that the sidecut describes equal the radius of the circle that the skis will necessarily inscribe on the snow in a "pure-carved turn"? In other words, will a ski with a "15-meter sidecut" always carve a 15-meter-radius arc?<<

While I agree this is indeed the heart of the discussion on this thread, the paraphrase
doesn't reflect my point with the radius vs. arc comment. That comment is related, but somewhat off-subject and could belong in an equipment thread.


Bob obviously understands that ARC and RADIUS are not interchangeable terms. This may seem like picking nits, but since I have realized so many people swap the terms I wonder if the technical specs of skis reflect it in some cases.

Back to the thread. Of course the ski will not always leave the same arc, even if it is perfectly carved. Skis are subject to too many variables, the human aboard being the most variable of variables.

The application of rotary or not is highly debatable since so many movements we make actually fall into all of the skills categories, increasing edge angle often involves a rotary movement of the leg, for ex., though it may not be its primary purpose. I do agree that the arc can be adjusted without necessarily using rotary input tho. But I'm not supposed to give an answer, right??

There we go again Robin. It is good to stay out of these. I might have to take a contract out on myself after my contributions to this one.
post #20 of 63
...nevermind...<FONT size="1">

[This message has been edited by Spyder (edited July 30, 2001).]</FONT>
post #21 of 63
OOOPS!! Just goes to show how I need to define my terms. I was actually talking about torque of the knees, not of the ski. So if the rotation happened JUST at the feet with no degree of through at the hip, I would guess the KNEE would be subject to torque.
But I also could be staying up too late with my text books and getting myself completely confused. Sorry! <FONT size="1">

[This message has been edited by Lisamarie (edited July 30, 2001).]</FONT>
post #22 of 63
>>OOOPS!! Just goes to show how I need to define my terms. I was actually talking about torque of the knees, not of the ski. So if the rotation happened JUST at the feet with no degree of through at the hip, I would guess the KNEE would be subject to torque.
But I also could be staying up to late with my text books and getting myself completely confused. Sorry! <<

LM
You are now officially recognized as an honorary Level III Certifiable PSIA Instructor. You can expect your pin, and feedback describing your performance in vague, non-specific and opinionated terms in 6 - 8 weeks.
post #23 of 63
HA!!! But there actually are some crazy people trying to talk me into going that route. I would need another 5 to 10 years to work on my technique before I even considered that!

------------------
Be Braver in your body, or your luck will leave you. DH Lawrence
post #24 of 63
Roto you said Is it just me or does anyone else have a problem with the term 'radius' applied to turns? Some people seem to think the term radius is directly interchangable with the term arc. Is that a separate thread?

Every circular (circular is the key word here) arc has a certain radius, just as any given radius will draw a circular arc. The smaller the radius, the "tighter" the arc. So in that sense, arc and radius are absolutely interchangeable. Of course, not all turns are circular, so I see where you are coming from.

My answer to Todd's question (although the answer came out in various instances):

To achieve a tighter turn with a ski, pressure the ski to bend it and create a tighter arc (or smaller radius). However, when pressure cannot be increased (such as on very hard snow), tip the ski and let the centrifugal forces and the shape of the ski bend that ski further. Of course, subtle rotational forces can be used as well to vary turn size, but if you are not in the "gang" you are not allowed to use such forces.
post #25 of 63
TomB

Yes, but if the radius is 15m the arc will not be 15m, it will be much longer. While they do share a constant relationship, you can't substitute one for the other mathematically or physically. One is a curve the other is a straight line. They are not interchageable. Who stops to turn around and look at their radii?

This is exactly what I am talking about. With the interchanging of the terms the meaning of radius may be getting bastardized. I just have to wonder if this is leeching its way into manufacturing specs. or at the very least into ski test results or buyers guide info.

OMG. I have to stop this. This is going to ruin me as a teacher and skier. I see myself spinning further and further down the toilet bowl of technoweenieism... help...gargle...glurp...must make turns... choke... strength failing against current... gasp... dizziness is ...swim!SWIMM!

someone throw me a rope!
post #26 of 63
Bob B: We are now on the same page! Whew! I think I'll just lurk for awhile on this one!<FONT size="1">

[This message has been edited by Lisamarie (edited July 30, 2001).]</FONT>
post #27 of 63
Roto you said: Yes, but if the radius is 15m the arc will not be 15m, it will be much longer

Sorry, but that is not correct. The length of the arc depends on the amount of rotation of the radius around a fixed point. The "tightness" of the arc (size of the turn) depends on the length of the radius from that fixed point.

However, regardless of the length of the arc, it is the same size radius that defines it. That is, if you rotate a 15m radius only 5 degrees, you will have far less arc-length than if you rotate it 90 degrees. But both in both cases you are tracing the same arc. But who cares, right?

In fact I suspect that the sidecuts of most skis are not circular arcs, but rather parabolic (which means that the radius changes for different sections of the side edge). Most certainly this is the case for the "Y-shape" skis.

Where is PhysicsMan when we need him?
post #28 of 63
Todd,
What's the answer you had in mind? It sounds like we all have our own opinion. What's yours since you asked the question?
post #29 of 63
OK so you can chop 15m out of a circle with a 15m radius, but that hardly equalizes arc and radius, thereby making them interchangeable. I ASSUMED arc to describe a completed turn performed on Alpine skis (on terrain of a pitch that would necessitate beginning and ending the turn perpendicular to the fall line for the resultant speed to remain roughly constant), theoretically a half circle. As always, ASSUMPTIONS are dangerous and leave too much room for interpretation......

Gurgle gurgle....swoosh....

Right, who cares...but this whole thing merely serves to intensify my question.

??
post #30 of 63
Bob,

Those Elan guys are smart! I never thought of it myself, but it does makes sense (at least in theory) that when you tip and bend a parabolic ski, the arc becomes more circular.

Cheers!
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